A medical imaging system comprises a microwave antenna array and an ultrasonic transducer array, and a processor (4) configured to process the received microwave signals and the received ultrasonic waves and generate an image of the internal structure of a body part, such as a breast (36). The ultrasonic transducers may be interspersed between the microwave antennae. The arrays may be formed on a substrate (18) contoured to conform to the body part. The microwave and ultrasound images may be spatially registered, and in particular be overlaid on one another to form a compound image. An actuator may be provided to move (e.g. rotate) the microwave antenna array and ultrasonic transducer array such as to position the plurality of microwave antennae and the plurality of ultrasonic transducers at previously unoccupied positions, thus creating a virtual array with a higher density of transceivers.
